A bored teenager might be forgiven for saying, "After 7 p.m., Seeley Lake is dead as a doornail." But what exactly is a doornail, and how did it become the epitome of dead things?
In the Medieval period and probably even earlier, a doornail was a hand-forged, iron nail with an extra-large head. Such a nail was hammered into a door consisting of vertical wood panels braced on the back by horizontal cross boards. The doornail was long enough that even after passing through both pieces of wood the sharp end protruded. The end was then bent over and hammered back into the wood, a process called clinching or clenching.
According to the "Morris Dictionary of Word and Phrase Origins," the technique was also called dead-nailing. Dead-nailing strengthened the door because it was virtually impossible to remove the nail. It also rendered the nail completely useless – or dead.
Another possible explanation comes from the website "Today I Found Out." Because of its large size the doornail "had to be 'hit on the head' with a hammer quite a few times more than your average nail. Because of the number of times it was hit, it would certainly be 'dead' by the time the head was flush to the wood of the door-that is, if it had been a living thing rather than an inanimate object."
Evidence of the phrase being used appears in the Middle English debate poem "Parliament of the Ages." Generally attributed to early fourteenth century, one line of the poem reads, "Dede as a dore-nayle doune was he fallen" [Dead as a doornail, down he fell].
The origin behind the meaning had already faded by the early nineteenth century when Dickens wrote:
"Old Marley was as dead as a door-nail. Mind, I don't mean to say that I know, of my own knowledge, what there is particularly dead about a door-nail. I might have been inclined, myself, to regard a coffin-nail as the deadest piece of ironmongery in the trade. But the wisdom of our ancestors is in the simile; and my unhallowed hands shall not disturb it, or the Country's done for. You will therefore permit me to repeat, emphatically, that Marley was as dead as a door-nail."